1. Field of the Invention
The present invention relates to a driving force interrupting mechanism.
2. Discussion of the Background
A conventional driving force interrupting mechanism configured as follows has been known (see, for example, Japanese Patent Application Publication No. 2006-218979). Specifically, in this mechanism, a driving shaft is provided between a drive source side and a final reduction gear unit provided on a wheel side. This driving shaft is divided into an input shaft and an output shaft. A coupling sleeve is movably fitted on these input and output shafts. When this coupling sleeve is fitted on only one of the input and output shafts, the transmission of the driving force to the final reduction gear unit is interrupted. On the other hand, when the coupling sleeve is fitted on both of the input and output shafts, the driving force is transmitted to the final reduction gear unit from the drive source side.
FIG. 5 and FIG. 6 of Japanese Patent Application Publication No. 2006-218979 will be described below.
The above-described mechanism for moving a coupling sleeve 162 includes: a first housing 153; a support shaft 261 rotatably attached to the first housing 153; a fork 164 swingably mounted on the support shaft 261, and connected to an outer circumference of the coupling sleeve 162; a first helical torsion spring 266 which biases the fork 164 in a direction of transmitting the driving force; and a second helical torsion spring 267 which biases the fork 164 in a direction of interrupting the driving force.
Swinging a lever 268 attached to an end portion of the support shaft 261 rotates the support shaft 261, thereby causing the fork 164 to swing in association with the first helical torsion spring 266. As a result, the coupling sleeve 162 moves. Because a male spline is formed on each of the aforementioned input and output shafts, the coupling sleeve is sometimes not fitted immediately on the other one of the input and output shafts depending on the rotational position of the corresponding male spline. In this case, the fork 164 swings only partway. However, the lever 268 and the support shaft 261 are capable of rotating further in association with the first helical torsion spring 266. What is achieved by the above mechanism is this rotation, that is, a lost motion, of the lever 268 and the support shaft 261 along with no swing of the fork 162 at this event.
The contents of Japanese Patent Application Publication No. 2006-218979 are incorporated herein by reference in their entirety.
The above-described driving force interrupting mechanism with the lost motion mechanism requires two helical springs, that is, the first helical torsion spring 266 acting in the direction of transmitting the driving force and the second helical torsion spring 267 acting in the direction of interrupting the driving force, and also requires components operating together with these springs. Accordingly, components are increased in number and complexity, thus occupying a large space in the first housing 153. As a result, the first housing 153 becomes large in size.